Food spoilage is a common problem in daily life. According to Food Science Australia and the national Cold Chain Center's estimation, 20 billion dollars are wasted globally each year due to spoilage of perishable foods during transportation and storage (Food Magazine, April 2006).
One of the major causes of food spoilage is growth of microorganisms in food products. Currently known microorganisms that cause food spoilage are fungi such as Geotrichum candidum, molds such as Aspergillus niger and Penicillium expansum, various yeasts, spoilage bacteria such as Alcaligenes faecalis, Bacillus stearothermophilus, Lactobacillus acidophilus and Pseudomonas fluorescens, pathogenic bacteria such as Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes, Yersinia enterocolitica, Salmonella typhimurium, Salmonella hydelberg, Salmonella enteritidis, Escherichia coli O157:H7, Campylobacter jejuni, Clostridium botulinum, Clostridium perfringens, Shigella sonnei, Shigella dysenteriae, Shigella flexneri, Shigella boydii, Vibrio cholera and Lysteria monocytogenes, and certain virus such as Norovirus and hepatitis virus.
People have been developing methods to prevent the growth of spoilage and pathogenic microorganisms in food products since the dawn of human history. A few well known examples of preserving perishable food products include: drying food including freeze drying beverages, salting food, smoking food, fermenting food, refrigerating food, freezing food, pickling food in syrup, sugar, oil, vinegar or alcohol and adding preserving chemicals such as sulfites, dehydroacetic acid, sodium nitrite, ethyl formate, propionic acid, sorbic acid, benzoic acid into food products.
New techniques to preserve food have been attempted and developed. For example, Nicolas Appert developed method of canning food in 1810. Louis Pasteur's research in 1864 led to the method of pasteurization dairy products. Both methods are still commonly used in food industry nowadays. U.S. Pat. No. 6,955,893 claims a method for preventing spoilage of food with lytic enzyme encoded by bacteriophage, and U.S. Pat. No. 5,654,020 discloses another method of using Lactobacillus AS-1 for inhibiting food spoilage.
Another popular anti-spoilage method is irradiation, which is exposing food to ionizing radiation by either gamma rays from radioactive Cobalt-60 or Cesium-137, high energy electrons, or x-rays. Irradiation kills bacteria, molds and insect pests in the food, slows down the ripening and spoiling of fruits, and induces seed sterility at higher doses. Irradiation becomes a major method used to prevent the growth of spoilage and pathogenic microorganisms in perishable food products after banning of methyl bromide fumigation in 2001. Food and Drug Administration (FDA) approved low-doses irradiation for wheat, wheat flour, and potatoes in the early 1960s. FDA approved the use of irradiation to control Salmonella and other harmful bacteria in chicken, turkey, and other fresh and frozen uncooked poultry in May 1990. In December 1997, FDA approved the use of irradiation to control pathogens in fresh and frozen red meats such as beef, lamb, and pork.
However, many food-preserving methods currently in use have their limitations. For example, nutritional value, density, texture and flavor of food may change if the food is dried, salted, smoked, fermented, pickled in syrup, sugar, oil, vinegar, and alcohol, or food preserving chemicals is added to the food. Frozen food and refrigerated food have to be kept in low temperature all the time. Irradiation cannot be used for all foods. It causes undesirable flavor changes in dairy products. Pasteurization eliminates all pathogens, but not all spoilage organisms are killed, since food is subjected to a lower heat treatment.
Food-preserving methods can be gauged by shelf life of the food product, which is the longer the shelf life the better the food-preserving method. Shelf life of food products is the length of time that perishable food products are suitable for sale or consumption before their quality is compromised by certain factors such as microorganism growth. Usually a label of “best before”, “use by” or “freshness date” followed by a date is put on packaged perishable food products, indicating their shelf life.
Prolonging the shelf life of food products is still an ongoing research subject. A new technology for preserving food has to meet certain requirements and standards. The food has to maintain its nutritional quality, flavor and safety after the treatment. If synthetic preservers are added to the food, they should be safe for human consumption with no long term adversary effect. Consumers are concerned with synthetic food additives, as well as many antibiotics for their long term effect to general health. Obviously antibiotics cannot be used as food addictives since their use will cause side effects such as allergies and disruption of normal bacterial flora in human body, and their long term use lead to bacterial resistance. Usually antibiotics may have odor, bitter taste or unpleasant color, making them unsuitable for food additives. On the other hand, some food products are fortified with vitamins and minerals, but those additives are not antimicrobials and have no effect to prolong the shelf life of the food products. Therefore there is a need to provide food additive that is natural, effectively antimicrobial and nutritional valuable.